This invention relates generally to filters suitable for eliminating unwanted noise occurring in electronic circuitry. More particularly, the present invention relates to a stand alone electro-magnetic interference filter which is mountable to a surface of a printed circuit board.
The operation of computers and other electronic devices is usually accompanied by unwanted noise generated in the same device or transmitted from another apparatus. As computing speeds increase, the demands and design requirements for printed circuit boards are becoming increasingly complex. The components on the printed circuit boards are becoming more sensitive to electro-magnetic interference and electrostatic discharge, both of which conditions are very undesirable and can interfere with proper operation of the printed circuit board.
One reason that electro-magnetic interference and electrostatic discharge are becoming problems in the operation of modern printed circuit boards is that the trend is to make the equipment, including the circuit board, smaller, thus putting radiating components in closer proximity to one another. Additionally, the explosion of wireless technology tends to jam the frequency spectrum. These factors, with others, points to a dramatic increase in electro-magnetic interference suppression requirements on equipment in many major electronics markets.
Filtered connectors, currently used in commercial and military applications, are standard connector configurations which have been modified to incorporate capacitors and/or inductive devices to accomplish electro-magnetic interference filtering. This is very costly and makes the connector a special order, custom product. Previously, in order to add a filtered connector in line between electronic components, an increase in case size, additional available space and special pins have often been required.
In general, electro-magnetic interference feed-through filtering capacitors have been provided primarily in connectors attaching various components to the outside case wall of the equipment. The purpose of these filtering connectors is to shunt unwanted noise to ground through the connector shell and ultimately to ground via the equipment housing. However, many connectors now used are non-metallic, and consequently there is no easy manner in which to shunt the noise through the connector shell to ground. Another problem encountered with existing technology is that typically only connector manufacturers have supplied filtered connectors. This has tied the OEM customer exclusively to one source and to one type of connector configuration.
Accordingly, there has been a need for a novel electro-magnetic interference suppressor which is adaptable to a number of different types of connector designs and configurations. Preferably such a suppressor should mount directly to the ground on the printed circuit board, providing the filter at the source of the electro-magnetic interference problem. Moreover, there is a need for an electro-magnetic interference suppressor that can also be utilized as an electrostatic discharge protection device when combined with other surface or printed circuit board mounted components. The improved suppressor/filter should be of simple construction and adaptable for use with different types of printed circuit boards and different types of connector leads. The present invention fulfills these needs and provides other related advantages.